Lateralized ultradian rhythms: evidence from tactile discrimination of either hand

Endogenous ultradian rhythms with periods of one or a few hours affect not only on physiological and behavioural functions but also perception and cognition. In particular, lateralized ultradian rhythms which seem to operate separately in the right and left hemispheres of the brain can be monitored by testing the tactile discrimination of the contralateral hand. The present paper is based on two subsequent studies: First, ultradian rhythms in tactile discrimination of either hand were examined in German subjects under laboratory conditions. Considerably different ultradian periods of right and left-handed tactile error rate were found in men but not in women. In a second study, a group of Kenyan Masai shepherds were tested while the subjects were leading herds on daily feeding routes through a savanna habitat. They showed ultradian periods of about 2 hours in tactile discrimination of either hand. Since the right hemisphere is specialized for visuospatial, the left for verbal processing lateralized ultradian rhythms may serve for a long-scale timing of neural processes underlying spatial and semantic mapping of the environment. Sex difference in German subjects and lateral differences found in left-handed (right-hemispheric) ultradian rhythms of German and Masai subjects are discussed from this point of view.